1. Field of the Invention
This invention relates to signal processing technology, and more particularly, to an apparatus and method for compensating signal attenuation based on an equalizer.
2. Description of Related Art
Signal transmission can be carried out through two kinds of channels: a cable channel or an air channel. In digital communication, channels can cause two kinds of degradation of transmission: signal attenuation and inter symbol interference (ISI). The former is from energy dispersed by the channel and the later is from bandwidth limitation of the channel. Sometimes, we use equalizers to overcome ISI and use auto-gain-control mechanism to compensate signal attenuation.
FIG. 1 is a schematic block diagram showing the architecture of a conventional apparatus for compensating signal attenuation. As shown, this apparatus includes a signal transmission channel 102 (which can be either a cable channel or an air channel), an auto gain controller 104, an A/D (analog-to-digital) converter 106, an equalizer 108, an accumulator 110, an averaging circuit 112, and an auto-gain-control mapping circuit 114. When an analog signal is transmitted through the signal transmission channel 102, it is subsequently amplified by the auto gain controller 104, and the amplified output is then transferred to the A/D converter 106 where it is converted into digital form. The output digital signal from the A/D converter 106 is then transferred both to the equalizer 108 and a feedback circuit consisting of the accumulator 110, the averaging circuit 112, and the auto-gain-control mapping circuit 114. The digital signal is first processed by the accumulator 110, and the output of the accumulator 110 is then processed by the averaging circuit 112. The output of the averaging circuit 112 is then transferred to the auto-gain-control mapping circuit 114 which is capable of outputting a gain value corresponding to the output value of the averaging circuit 112 and sending this gain value to the auto gain controller 104 to correspondingly adjust the gain of the auto gain controller 104. This feedback control continues until the equalizer 108 receives the desired digital signal amplitude.
One disadvantage of using the forgoing apparatus, however, is that the accumulator 110 needs a great amount of signal amplitude values to compute for the incoming signal amplitude, which is a time-consuming procedure, making the overall operation quite inefficient. Moreover, since the output digital signal from the A/D converter 106 would be ISI degraded, it would not allow the subsequent feedback circuit, including the accumulator 110, the averaging circuit 112, and the auto-gain-control mapping circuit 114, to obtain an accurate result to control the gain of the auto gain controller 104.
In conclusion, the conventional apparatus has the following drawbacks:
First, it would need storing a great amount of signal amplitude values to compute for the incoming signal amplitude, which is a time-consuming procedure, making the overall operation quite inefficient.
Second, since the signal would be subjected to ISI degradation, it would result in an inaccurate gain control.
Third, when the gain of the auto gain controller 104 comes to a fixed value, it would nevertheless requires the pre-evaluation of an initial weight value for the equalizer 108, which would not be easy to accurately carry out.